Known various physical quantity sensors convert an amount of mechanical displacement corresponding to a physical quantity from the outside into an electric signal to thereby detect a physical quantity. For example, an acceleration sensor takes out, as an electric signal, a change in electrostatic capacitance between a movable electrode displaced according to acceleration and a fixed detection electrode in a detection element and thereby detects acceleration. (refer to, for example, Patent Document 1; JP-7-306222-A)
Although each of these physical quantity sensors converts the change in the electrostatic capacitance of the detection element into the electric signal using the capacitance detection circuit, a portion (hereinafter called a capacitance detection input section) at which the detection element is connected with the capacitance detection circuit is brought to electrically high impedance. For this reason, the physical quantity sensor is weak to electromagnetic or electrostatic externally-incoming noise. Therefore, as described in the Patent Document 1, a grounded conductive member covers the detection element to serve as an electromagnetic shield, thereby achieving a reduction in the externally-incoming noise.